Playlist Magazine suggests using an old (or current) iPod as a backup bootable disk for your Mac.

To get it going you'll need to set your iPod to run in disk mode, and then install OS X on it using the original installation disks. If you're willing to lay out some cash for extra bootable iPod features, pricey software Protogo ($135, yikes!) can boot several versions of OS X from your iPod, as well as add various utilities. If you've already got a bootable disk, like DiskWarrior, the free Dasboot can also get the job done. For more boot disk love, see also our top 10 system recovery tools.